首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 42 毫秒
1.
The Central Rift Valley (CRV) is one of the most environmentally vulnerable areas of Ethiopia. Most of the lowland in the CRV is arid or semiarid, and droughts occur frequently. We studied the dynamics of land use and cover and land degradation by analyzing Landsat data from 1973, 1985, and 2006 using Geographic Information Systems and remote sensing techniques. The analysis revealed that in the last 30 years, water bodies, forest, and woodland decreased by 15·3, 66·3, and 69·2 per cent, respectively; intensive cultivation, mixed cultivation/woodland, and degraded land increased by 34·5, 79·7, and 200·7 per cent. The major causes of land use and cover change (LUCC) and land degradation in the area were population and livestock growth in regions of limited resources, unsustainable farming techniques, the Ethiopian land tenure system and poverty. Lake level and area decline, and accelerated land degradation are the major environmental impacts of LUCC observed in the CRV. The environmental and socio‐economic consequences of LUCC and land degradation are far‐reaching. As a result of the expansion of land degradation over time, agricultural productivity has decreased and worsened food insecurity (shortages) and poverty in the Ethiopian CRV. In addition, if current trends in LUCC continue, Lake Abiyata will dry up by 2021. A detailed study of the degradation amount in relation to soil erosion, sediment yield to the lakes and catchment characteristics should be made using adaptable models; so as to guide the implementation of comprehensive and sustainable land use management by giving more attention to erosion prone areas. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
Rehabilitating degraded rangelands using enclosures offers various benefits to agro‐pastoral households. However, enclosure benefits cannot be generalized as there are variations across dryland ecosystems and societies. This study assessed the qualitative and quantitative benefits derived from rehabilitating degraded rangelands using private enclosures in Chepareria, West Pokot County, Kenya. Dry‐season grazing reserves, healthier livestock, improved livestock productivity, easier livestock management, food security, reduced animal losses, ecosystem services, land ownership, independence and improved standard of living were the main qualitative benefits from private enclosures identified. Quantitative benefits were manifested through various enclosure enterprise combinations, sale of enclosure marketable products and adoption of alternative income generating activities. They included the sale of livestock and livestock products, maize, wood cutting, grass cuttings, contractual grazing, grass seeds, poultry products, fruits and honey, amongst others. Livestock production directly accounts for 42·4% of the total enclosure income and is the main source of livelihood in Chepareria. There was a significant trend of increasing total enclosure income with enclosure acreage (p ≤ 0·05) while enclosure age was insignificant. Enclosures cushion households against climatic shocks such as drought by providing additional flexibility in land, fodder, livestock management and the uptake of various income generating activities. We conclude that enclosures have the potential of contributing to resilience as attested from the benefits reported in this study. However, private enclosure tradeoffs such income differentiation, reduced communal land and conflict have implications on how the ecological and socio‐economic aspects may be impacted as the establishment of private enclosures in Chepareria continues. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

3.
When farmers migrate yearly to a village to carry out intense farming during the rainy season, and thereafter return to a more permanent place of abode this is referred to as seasonal migration. The impact of such migration on land‐use/land‐cover change in an area within the Volta Basin of Ghana was examined using satellite image analysis and socioeconomic surveys. The most drastic land‐cover change involved the conversion of woodland to agricultural land, while there was also a general transition to less vegetation cover. Socioeconomic surveys revealed that most of the migration occurred during the post‐structural adjustment period in Ghana with declining soil fertility accounting for the highest per cent of causes of migration. Multiple regression results highlighted the role of population size and distribution, marketing of agricultural produce and technological evolution of the household in determining agricultural land‐use change. Policy initiatives that could lead to environment conservation are suggested. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

4.
Lake Qinghai, the largest saline lake in China, covers 4234 km2 (2007) with a catchment area of 29 660 km2 on the northeastern margin of the Qinghai‐Tibet Plateau. The ecosystem of the lake is extremely vulnerable and sensitive to global climate change and human interference. However, little information is available on land use/cover change (LUCC) in Lake Qinghai watershed. Using a geographical information system (GIS) and remote sensing (RS), this study analysed land use and land cover change pattern in Lake Qinghai watershed between 1977 and 2004 and discussed major environmental issues in this area. LUCC analysis indicated that grassland (63 per cent) and water body (18 per cent) dominated in the watershed and the magnitude of the land use and land cover change was generally low; the percentage of the change of various land types relative to the total area was less than 1 per cent. From 1977 to 2004, cropland, sandy land, bare rock, salinized land, swampland and built‐up areas increased by 0·43, 0·35, 0·24, 0·06, 0·03 and 0·03 per cent of the total area, respectively; in contrast, water body, grassland and woodland decreased by 0·99, 0·22 and 0·05 per cent, respectively. Moreover, the area of LUCC tended to expand from places around the lake to the upper reaches of the watershed during the last three decades. The LUCC transition pattern was: woodland converted to grassland, grassland converted to cropland and water body converted to sandy land. Lake level decline and grassland degradation are major ecological and environmental problems in Lake Qinghai watershed. The level and area of the lake decreased at the rate of 6·7 cm a−1 and 6·4 km2 a−1, respectively, between 1959 and 2007, resulting in sandy land expansion and water quality deterioration. Lake level decline and area shrinkage was mainly attributed to climate change, but grassland degradation was mainly resulted from anthropogenic activities (increasing population, overgrazing and policy). Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

5.
No‐till, crop diversity and integrated crop–livestock systems are proposed managements to increase agriculture sustainability in the rice paddies of the Southern Brazilian lowlands and avoid degradation in the region. Because soil is considered a key medium in which management modifications can be measured, our study aimed to evaluate soil‐quality impacts by measuring carbon and nitrogen stocks and microbial activity 18 months after the adoption of different paddy‐farming systems in an Albaqualf soil of Southern Brazil. The treatments consisted of five paddy‐farming systems with a range of vegetation diversity (both in time and in space) and grazing seasons. In addition, a reference area (i.e. native forest) was sampled for comparison. We verified that soil quality was affected over the short term through the adoption of no‐till, crop diversity and integrated grazing practices. However, during the study period, only the system with low anthropic and/or mechanical intervention and high plant diversity differed from the traditional paddy land‐use approach in Brazil in terms of soil‐quality effects. This system achieved a carbon management index of 49 (approximately half that of the native forest) and had the highest enzymatic activity (similar to native forest). These outcomes were primarily due to an increase in the particulate organic matter fraction of the soil carbon stock (4·6 Mg ha−1 more than in rice monocropping). To evaluate changes in soil quality over the long term, additional studies are required. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

6.
Assessments of the effects of deforestation, post-clearance tillage methods and farming systems treatments on soil properties were made from 1978 through 1987 on agricultural watersheds near Ibadan, southwestern Nigeria. These experiments were conducted in two phases: Phase I from 1978 through 1981 and Phase II from 1983 to 1987, with 1 year (1982) as a transition phase when all plots were sown with mucuna (Mucuna utilis). There were six treatments in Phase I involving combinations of land clearing and tillage methods: (1) manual clearing with no-till (MC-NT); (2) manual clearing with plough-till (MC-PT); (3) shear-blade clearing with no-till (SB-NT); (4) tree-pusher/root rake clearing with no-till (TP-NT); (5) tree-pusher/root-rake clearing with plough-till (TP-PT); (6) traditional farming (TF). The six treatments were replicated twice in a completely randomized design. The traditional treatment of Phase I was discontinued during Phase II. The five farming systems studied during Phase II with a no-till system in all treatments were: (1) alley cropping with Leucaena leucocephala established on the contour at 4-m intervals; (2) and (3) fallowing with Mucuna utilis on severely degraded and moderately degraded watersheds, respectively, for 1 year followed by maize-cowpea rotation for another; (4) and (5) ley farming involving establishment of pasture in the first year on severely and moderately degraded plots, respectively, controlled grazing in the second year, and growing maize (Zea mays)-cowpea (Vigna unguiculata) in the third year. All treatments, imposed on watersheds of 2–4 ha each, were replicated twice. The soil properties analyzed were particle size distribution, total aggregation and mean weight diameter of aggregates, soil bulk density, penetrometer resistance, water retention characteristics, infiltration capacity and saturated hydraulic conductivity. These properties were measured under the forest cover in 1978, and once every year during the dry season thereafter during Phases I and II. Prior to deforestation, mean soil bulk density was 0·72 Mg m−3 and 1·30 Mg m−3, soil penetration resistance was 32·4 KPa and 90·7 KPa, and mean weight diameter of aggregates was 3·7 mm and 3·2 mm for 0–5 cm and 5–10 cm depths, respectively. The infiltration rate was excessive (54–334 cm hr−1) and saturated hydraulic conductivity was rapid (166–499 cm hr−1) under the forest cover. Furthermore, water transmission properties varied significantly even over short distances of about 1 m. Deforestation and cultivation increased soil bulk density and penetration resistance but decreased mean weight diameter of aggregates. One year after deforestation in 1980, mean soil bulk density was 1·41 Mg m−3 for 0–5 cm depth and 1·58 Mg m−3 for 5–10 cm depth. Soil bulk density and penetration resistance were generally higher for NT than for PT methods, and the penetration resistance was extremely high in all treatments by 1985. During Phase II, soil bulk density was high during the grazing cycle of the ley farming treatment. Sand content at 0–5 cm depth increased and clay content decreased with cultivation duration. Soon after deforestation, saturated hydraulic conductivity and equilibrium infiltration rate in cleared and cultivated land declined to only 20–30 per cent of that under forest. Mean saturated hydraulic conductivity following deforestation was 46·0 cm hr−1 for 0–5 cm depth and 53·7 cm hr−1 for 5–10 cm depth. Further, infiltration rate declined with deforestation and cultivation duration in all cropping systems treatments. During Phase I, mean infiltration rate was 115·8 cm hr−1 under forest cover in 1978, 20·9 cm hr−1 in 1979, 17·4 cm hr−1 in 1980 and 20·9 cm hr−1 in 1981. During Phase II, mean infiltration rate was 8·5 cm hr−1 in 1982, 11·9 cm hr−1 in 1983, 11·0 cm hr−1 in 1984, 11·3 cm hr−1 in 1985 and 5·3 cm hr−1 in 1986. Infiltration rate was generally high in ley farming and mucuna fallowing treatments. Natural fallowing drastically improved the infiltration rate from 19·2 cm hr−1 in 1982 to 193·2 cm hr−1 in 1986, a ten-fold increase within 5 years of fallowing. High-energy soil water retention characteristics in Phase I were affected by those treatments that caused soil compaction by mechanized clearing and no-till systems. Soil water retention at 0·01 MPa potential in 1979 was 19·2 per cent (gravimetrics) for SB, 17·9 per cent for TP, 15·9 per cent for MC and 17·8 per cent for TF methods. With regards to tillage, soil water retention was 17·8 per cent for NT compared with 16·8 per cent for PT. During Phase II, water retention characteristics were not affected by the farming system treatments. Mean soil water retention (average of 4 years' data from 1982 to 1986) at 0·01 MPa for 0–5 cm depth was 16·6 per cent for alley cropping, 16·7 per cent for mucuna fallowing and 16·8 per cent for ley farming. Mean soil water retention for 1·5 MPa suction was 9·3 per cent for alley cropping, 8·7 per cent for mucuna fallowing, and 9·3 per cent for ley farming. Water retention at 1·5 MPa suction correlated with the clay and soil organic carbon content.  相似文献   

7.
In arid and semi‐arid regions, water erosion is difficult to model because of highly irregular precipitation regimes and changes in vegetation cover. The application of quantitative, process‐based models at the catchment scale is often problematic because of large data requirements. Qualitative methods require less data and can be more easily performed in a relatively short time, but they are more subjective. The objective of this research is to develop an erosion assessment methodology that combines qualitative field surveys with quantitative model estimates. The qualitative World Overview of Conservation Approaches and Technologies (WOCAT) methodology is based on expert observations per mapping unit, while the Pan‐European Soil Erosion Risk Assessment (PESERA) model simulates hill slope soil loss based on land cover, soil texture, meteorological data and slope profile. This study was conducted in the 106·4‐km2 Peristerona watershed in Cyprus with a mean local slope higher than 40% in the mountainous upstream area and less than 8% in the plain. Out of 68 units, PESERA and WOCAT results were in agreement in 40 units, while PESERA results were lower in 25 and higher in 3 units. Both methods identified burnt areas and complex cultivation patterns as the most degraded. The total PESERA‐based sediment yield for the watershed was 1·2 Mg ha−1 y−1, which fell within the range of the sediment yield measured at the check‐dam downstream (0·2–2 Mg ha−1 y−1). This study provides a linkage between qualitative and quantitative soil erosion methods and helps to translate the outcomes of the former into the latter, thus providing a good tool for local erosion assessment. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

8.
Tropical mangrove forests can play an important role in the functioning of adjacent marine ecosystems, by protecting them from an excess in land‐derived sediment and nutrients. The strength of this interaction may however depend on the nutrient status of the mangrove forest. This study related the nutrient status of eight mangrove forests in Phang Nga Bay (Thailand) to the land‐cover distributions in the upstream catchment areas. Nutrient status was assessed using indicators integrating over short (porewater and sediment nutrient composition) and long timespans (mangrove leaves and sesarmid crab tissue characteristics). Using multivariate statistics (PCA analysis), these nutrient status data were then related to the land cover data, which were obtained through the analysis of satellite imagery. Nutrient availability was lowest for mangroves in catchments with large natural vegetation cover and was elevated in catchments with increasing levels of anthropogenic influence. Furthermore, nutrient availability was significantly correlated with several forms of land use, including natural forest, rice paddies, cleared ground and urban areas. While all indicators supported these results, relationships were strongest for long‐term indicators. Information on the relationship between land use in the catchment area and mangrove nutrient status may be important for the effective management of this habitat, as well as adjacent marine systems. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
The combined effects of erosive rains, steep slopes and human land use have caused severe land degradation in the Ethiopian Highlands for several thousand years, but since the 1970s, however, land rehabilitation programmes have been established to try to reverse deterioration. In order to characterize and quantify the transformations in the north Ethiopian Highlands, a study was carried out over 8884 km2 of the Tigray Highlands of northern Ethiopia. Using Landsat Multispectral Scanner and later Thematic Mapper imagery (1972, 1984/1986 and 2000), historical terrestrial photographs (1974–1975) and fieldwork (2008), we prepared land use and cover maps. For assessing the use of the historical terrestrial photographs, Landsat images from 1972 were classified using two different methods, namely conventional change detection (image differencing) and ground truthing (using the historical photographs of 1974–1975). Results show that the use of terrestrial photographs is promising, as the classification accuracy based on this method (Kappa coefficient 0·54) is better than the classification accuracy of the method based on image differencing (Kappa coefficient 0·46). Major land use and cover changes indicate the following: (1) a gradual but significant decline in bare ground (32 per cent in 1972 to 8 per cent in 2000); (2) a significant increase of bushland (25 to 43 per cent) and total forest area (including eucalypt plantations, 2·6 to 6·3 per cent); and (3) creation of numerous lakes and ponds. The dominant change trajectory (27 per cent of the study area) indicates a gradual or recent vegetation increase. These changes can be linked to the population growth and the introduction of land rehabilitation initiatives, complemented by growing awareness of land holders. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

10.
Impact assessments on river systems of the combined effect of bed and suspended sediment loads from quarries are difficult to find. In this study, bed and suspended loads were measured to determine the impact of a 20‐ha limestone quarry on the river system of its 5,000‐ha steep, diverse land use/land cover but mostly forested catchment. A network of hydrologic and sediment monitoring instruments was deployed over the catchment during two separate study periods when sediment loadings were measured from captured storms. Results showed that the quarry stood to make a disproportionately large contribution to the catchment's estimated 2·1 Mg ha−1 yr−1 suspended sediment load. Large storm events contributed most of the loadings with five events supplying 92% of total loadings at the outlet. A paired method approach to compare suspended sediment loads between two subcatchments showed that during eight storm events, the quarry yielded between 2 and 49·2 Mg ha−1 per event, whereas the forest never yielded more than 0·1 Mg ha−1. Furthermore, the contribution of sediments from the quarry to bed load was more than 75% at a section located 1·2 km downstream. Future management activities to reduce sediment and bed loads, not only from this catchment but also from all others with similar land use/land covers, should focus on improving quarry operations. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

11.
Land‐use dynamics in drylands are complex processes. In the context of a typical agropastoral village in northwestern Syria Im Mial, the effects of demographic and social changes, reduced soil productivity, changes in agricultural technologies and historical events on land use and land productivity are examined. Decreasing yields, mainly the result of reduced fallow periods and low investments in the land, and the deterioration of the grazing resources are the two main signs of the loss of land productivity in the area. The growing population forces the villagers to practise continuous rainfed barley cultivation with no or only occasional fallow, and without any application of plant nutrients. Also, technological changes, from the use of donkey ploughs and hand harvesting to less labour‐intensive and time‐consuming cultivation practices with tractors and combine harvesters, and the increased importance of stubble in the livestock diet have contributed to the reduction of the fallow periods. The villagers attribute the yield decreases mainly to the low rainfall in the area. The high rainfall variability discourages the fallowing of fields because continuous cultivation maximizes the chances for good harvests in years with high rainfall. There is also an expansion of cultivation into the less fertile and sloping traditional grazing areas. Population growth, increased numbers of livestock and the expansion of cultivated land into grazing areas has also put pressure on the grazing resources of the village. The possession of livestock is seen as a sign of wealth and the villagers aim to have large flocks of animals. For them, livestock is also an important means for investment of cash earned from off‐farm work, which is the main source of income for most of the households in the village. There is a recent trend of increasing levels of crop‐livestock integration with less free grazing that produces higher return to the land users. This may also have a positive effect on the restoration and conservation of the degraded natural traditional grazing grounds. The stabilization and productive use of the land resources in this dry environment requires the combined and interdisciplinary effort from both the land‐users and the policy‐makers. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

12.
Better understanding of how the loess soils respond to topography and land use under catchment‐scale vegetation restoration is needed to enable science‐based land management interventions for the policy‐driven “Grain‐for‐Green” eco‐restoration program in the Loess Plateau of China. The objective of this study was to characterize the relationships of four selected soil quality indicators to land use under vegetation restoration and topography for a small catchment (0·58 km2) in the Loess Plateau. The major land uses established in the catchment are cropland, fallow (i.e., natural revegetation), grassland, and jujube orchard. The four soil quality indicators were soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), and mean root zone soil water content during the wet season (MRZSWwet). SOC, STN, and MRZSWwet were significantly different (p < 0·05) for different land uses. Grassland showed the highest values for these three properties, whereas cropland had relatively low values for SOC and STN. Land use had no effect on STP, although the lowest value was observed in grassland. Spatial analysis showed that various relations between soil quality indicators and topography (slope and elevation) were observed. These relations were generally weak for most of them, and they varied with land uses. Further analyses indicated that land uses, slope, and elevation had significant effects on the relations between different soil quality indicators. The results here should provide useful information for the further development of “Grain‐for‐Green” program. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

13.
The West Asia–North Africa (WANA) region has a land area of 1.7 billion ha, and a population of 600 million. Desertification and soil degradation are severe problems in the region. The problem of drought stress is exacerbated by low and erratic rainfall and soils of limited available water holding capacity and soil organic carbon (SOC) content of less than 0.5 per cent. The SOC pool of most soils has been depleted by soil degradation and widespread use of subsistence and exploitative farming systems. The historic loss of a SOC pool for the soils of the WANA region may be 6–12 Pg compared with the global loss of 66–90 Pg. Assuming that 60 per cent of the historic loss can be resequestered, the total soil‐C sink capacity of the WANA region may be 3–7 Pg. This potential may be realized through adoption of measures to control desertification, restore degraded soils and ecosystems, and improve soil and crop management techniques that can enhance the SOC pool and improve soil quality. The strategies of soil‐C sequestration include integrated nutrient management (INM) and recycling, controlled grazing, and growing improved fodder species on rangeland. Improved technologies for cropland include use of INM and biofertilizers, appropriate tillage methods and residue management techniques, crop rotations and cover crops, and water and nutrient recycling technologies. Through adoption of such measures, the potential of soil‐C sequestration in the WANA region is 0.2–0.4 Pg C yr−1. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

14.
Abstract. The Pilot Nitrate Sensitive Areas Scheme was set up in England in 1990 to test measures aimed at reducing nitrate losses from agricultural land. Ten groundwater catchments were chosen to typify the geology and farming of areas where nitrate concentrations in abstracted water were high. Voluntary and compensated controls on farming, based on recent research, were introduced. Scheme membership was for 5 years from 1990 or 1991, and 86% of the agricultural land entered the Scheme. On all farms entering the Scheme, manure and fertilizer use were restricted and green cover crops were required over winter (Basic Scheme). Additional payments were available for conversion of arable land to zero or low-input grassland (Premium Scheme). Intensive pig and poultry farmers were assisted with the costs of transporting manure for spreading over a wider area. The most effective changes were improved management of livestock manures, especially of the very large local quantities from housed pig or poultry units; conversion of arable land to low-input grassland; and use of cover crops. There were no indications of reduced crop yields but some requirements increased costs and management complexities. Estimates based on both model calculations and measurements indicated that nitrate losses from agricultural land decreased by about 30%, with considerable variation between areas.  相似文献   

15.
The lower Himalayan regions of north‐west India experienced a severe land‐use change in the recent past. A study was thus conducted to assess the effect of grassland, forest, agricultural and eroded land uses on soil aggregation, bulk density, pore size distribution and water retention and transmission characteristics. The soil samples were analysed for aggregate stability by shaking under water and water drop stability by using single simulated raindrop technique. The water‐stable aggregates (WSA) >2 mm were highest (17·3 per cent) in the surface layers of grassland, whereas the micro‐aggregates (WSA < 0·25 mm) were highest in eroded soils. The water drop stability followed the similar trend. It decreased with the increase in aggregate size. Being lowest in eroded soils, the soil organic carbon also showed an adverse effect of past land‐use change. The bulk density was highest in eroded lands, being significantly higher for the individual aggregates than that of the bulk soils. The macroporosity (>150 µm) of eroded soils was significantly (p < 0·05) lower than that of grassland and forest soils. The grassland soils retained the highest amount of water. Significant (p < 0·05) effects of land use, soil depth and their interaction were observed in water retention at different soil water suctions. Eroded soils had significantly (p < 0·05) lower water retention than grassland and forest soils. The saturated hydraulic conductivity and maximum water‐holding capacity of eroded soils were sufficiently lower than those of forest and grassland soils. These indicated a degradation of soil physical attributes due to the conversion of natural ecosystems to farming system and increased erosion hazards in the lower Himalayan region of north‐west India. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
Annual soil losses in southern Italy can exceed 100–150 t ha− 1 year− 1. Where erosion on agricultural land is particularly severe, land use change and afforestation are frequently seen as the most appropriate means of reducing erosion risk. However, the overall effectiveness of afforestation in reducing soil erosion remains uncertain, due to the poor development of the forest cover in some areas, leading to significant areas with sparse tree cover, and the erosional impact of forest harvesting, which commonly involves clearcutting. The study reported here addresses this uncertainty and focuses on two small catchments (W2 and W3) located in Calabria, southern Italy, for which measurements of suspended sediment yield are available. Both the catchments originally supported a rangeland vegetation cover and they were planted with eucalyptus trees in 1968. Currently, only catchment W3 supports a continuous forest cover. In catchment W2 the forest cover is discontinuous and there is a significant area of the catchment (ca. 20%) where the tree cover is sparse and the vegetation cover is dominated by natural grasses. Two additional erosion plots were established within catchment W2 in 1991, in order to explore the effect of the density of the tree cover on soil erosion. Information on the sediment yields from the two catchments and the plots for 10 storm events that occurred during the period December 2005–December 2006 and associated information on the 137Cs and excess 210Pb of the sediment, have been used to investigate the effectiveness of afforestation in reducing sediment mobilisation and net soil loss from the catchments involved. The results demonstrate that the areas of greatest soil loss are associated with the slopes where the tree cover is discontinuous, and that forest harvesting by clearcutting causes significant short-term increases in sediment mobilisation and sediment yield. These findings, which are consistent with previous work undertaken within the same area, emphasize the importance of vegetation cover density in influencing rates of soil loss in the study catchments. The study also provided a useful demonstration of the potential for using measurements of the 137Cs and 210Pbex content of sediment, in combination with more traditional sediment monitoring, to investigate sediment sources and to compare the sediment dynamics of catchments subjected to different land management practices.  相似文献   

17.
The effect of soil management and land use change are of interest to the sustainable land management for improving the environment and advancing food security in developing countries. Both anthropogenic changes and natural processes affect agriculture primarily by altering soil quality. This paper reviews and synthesizes the available literatures related to the influence of soil management and land use changes on soil carbon (C) stock in Ethiopia. The review shows that topsoil C stock declines approximately 0–63%, 0–23%, and 17–83% upon land use conversion from forest to crop land, to open grazing, and to plantation, respectively. An increase of 1–3% in soil C stock was observed within 10 years of converting open grazed land to protected enclosures. However, there was a little change in soil C stock below 20 cm depth. There is a large potential of increasing SOC pool with adoption of land restorative measures. Total potential of soil C sequestration with the adoption of restoration measures ranges 0·066–2·2 Tg C y−1 on rain‐fed cropland and 4·2–10·5 Tg C y−1 on rangeland. Given large area and diverse ecological conditions in Ethiopia, research data available in published literature are rather scanty. Therefore, researchable priorities identified in this review are important. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

18.
Vegetation restoration efforts (planting trees and grass) have been effective in controlling soil erosion on the Loess Plateau (NW China). Shifts in land cover result in modifications of soil properties. Yet, whether the hydraulic properties have also been improved by vegetation restoration is still not clear. The objective of this paper was to understand how vegetation restoration alters soil structure and related soil hydraulic properties such as permeability and soil water storage capacity. Three adjacent sites with similar soil texture, soil type, and topography, but different land cover (black locust forest, grassland, and cropland) were selected in a typical small catchment in the middle reaches of the Yellow River (Loess Plateau). Seasonal variation of soil hydraulic properties in topsoil and subsoil were examined. Our study revealed that land‐use type had a significant impact on field‐saturated, near‐saturated hydraulic conductivity, and soil water characteristics. Specifically, conversion from cropland to grass or forests promotes infiltration capacity as a result of increased saturated hydraulic conductivity, air capacity, and macroporosity. Moreover, conversion from cropland to forest tends to promote the creation of mesopores, which increase soil water‐storage capacity. Tillage of cropland created temporarily well‐structured topsoil but compacted subsoil as indicated by low subsoil saturated hydraulic conductivity, air capacity, and plant‐available water capacity. No impact of land cover conversion on unsaturated hydraulic conductivities at suction > 300 cm was found indicating that changes in land cover do not affect functional meso‐ and microporosity. Our work demonstrates that changes in soil hydraulic properties resulting from soil conservation efforts need to be considered when soil conservation measures shall be implemented in water‐limited regions. For ensuring the sustainability of such measures, the impact of soil conversion on water resources and hydrological processes needs to be further investigated.  相似文献   

19.
Continued conversion of woodlands into grazing and farmland is seriously undermining the natural ecosystem of the dry and fragile Rift Valley areas of Ethiopia. This study investigated the effects of land‐use change on soil organic carbon (SOC), total nitrogen (N), pH, exchangeable bases, cation exchange capacity (CEC) and base saturation (per cent) in three adjacent land‐use types: controlled grazing, open‐grazing and farmland. A total of 81 soil samples were collected and analysed. Contents of SOC and total N decreased drastically in open‐grazing and farmland (p < 0·001), and were significantly higher in the top 0·2 m than in the subsurface soil layer. Compared with the controlled grazing, reductions in the contents of SOC and total N in the top 1 m soil layer were 22–30 and 19 per cent, respectively, due possibly to the decrease in plant biomass input into the soil and the fast decomposition of organic materials. Long‐term cultivation had significantly increased the concentration of exchangeable K. Exchangeable Na was high in the lower layers, while Mg was higher in the top surface soil. CEC also varied with soil depth (p = 0·016); it was higher in the topsoil than in the subsurface soil, which may be, among others, due to the differences in soil organic matter distribution with depth. Although these semi‐arid soils are known to have low organic carbon and CEC levels, the values from the current study area are critically low, and may indicate the further impoverishment of the soils under high agricultural and grazing pressures. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
The application of fractal geometry to describe soil degradation and dynamics is becoming a useful tool for better understanding of the performance of soil systems. In this study, four different land cover types, which represent a sequence of grass–desert shrub transition and a gradient of desertification, were selected, and soils at depths of 0–10, 10–20 and 20–40 cm were sampled in the Ordos Plateau of Inner Mongolia, PR China. The fractal theory was used to analyse the soil particle‐size distribution (PSD) and its variations. The results showed that (i) vegetation conversion and desertification significantly changed the soil PSD. During the desertification process, soil coarse fractions that ranged from 250 to 100 µm significantly increased, whereas fine fractions lower than 50 µm significantly decreased (p < 0·01); (ii) fractal model of the accumulative volume particle‐size distribution is appropriate, and fractal dimensions (Dm) of soil PSD significantly decreased along the sequence of grass–desert shrub transition; (iii) Dm is more sensitive to the desertification process, and therefore, we suggest Dm other than soil texture and soil organic carbon as a reliable parameter to reflect the soil environment change induced by desertification. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号